The lining of the walls of the small intestine includes small pits, called the crypts of Lieberkühn, that lie between the intestinal villi. The crypts produce the four cell types of villi: enterocytes, goblet cells, enteroendocrine cells, and Paneth cells. The mucus of the goblet cells lubricates and protects the surfaces of the bowel lumen. The enterocytes of the crypts secrete large quantities of water and electrolytes, and those of the villi reabsorb water and electrolytes along with the products of metabolism. The enteroendocrine cells secrete hormones into the bloodstream, and the Paneth cells produce antimicrobial peptides and growth factors (Lingappa, 2003). Active secretion that overwhelms the absorptive processes of the GI tract leads to diarrhea that generally persists with fasting (Mercadante, 2002). Substances that increase bowel secretions (secretagogues) include vasoactive intestinal polypeptide, calcitonin, serotonin, bradykinin, substance P, prostaglandins, and gastrin (Levy, 1991; Lingappa, 2003; Mercadante, 2002). Conditions that lead to the production of one or more of these secretagogues include the following:

The small bowel is highly permeable to sodium and water transport but not to solute. When large amounts of nonabsorbable sugar (e.g., lactulose and sorbitol) are ingested, the ability of the GI tract to compensate may be overwhelmed, resulting in diarrhea from the osmosis of fluid into the lumen. The diarrhea due to carbohydrate malabsorption is characterized by a low pH, high content of carbohydrates, high stool osmolality, and flatulence. Other substances that cause osmotic diarrhea are magnesium, sulfate, and poorly absorbed salts, including bile salts. The pH of diarrhea caused by one of these latter substances is usually normal (Mercadante, 2002).

Persons with lactose intolerance and those receiving high-carbohydrate supplements or enteral feedings are at risk for osmotic diarrhea. The sorbitol in sugar-free elixirs and enteral feedings is often overlooked as a cause of this symptom (Sykes, 2003). The overuse of osmotic laxatives is also a cause of diarrhea for some persons with advanced disease.

Malabsorption of fat is another cause of osmotic diarrhea. Most dietary intake of fat is absorbed in the small intestines and only small amounts of lipids enter the colon. The absorption of fat from the small intestines is dependent on pancreatic enzymes to break down the fats and bile salts to make the fat particles soluble. Pancreatic cancer or resection of the pancreas may cause a deficiency of pancreatic enzymes, leading to malabsorption of fat and steatorrhea. Biliary tract obstruction, terminal ileal resection, and cholestatic liver disease cause a decrease in bile salt formation, again contributing to malabsorption of fat and steatorrhea (Mercadante, 2002). Steatorrhea is characterized by loose, pale, foul-smelling feces. The feces may be greasy in appearance and tend to float in the toilet, making them difficult to flush.

When GI tract motility is abnormally stimulated, bowel contents are moved through the intestines too quickly to prevent adequate absorption, leading to diarrhea. Several factors may contribute to GI hypermotility.

Parasympathetic stimulation enhances GI motility and leads to diarrhea. Both the small and the large intestines receive parasympathetic stimulation from the vagus and the hypogastric plexus. Stimulation of the sympathetic nervous system inhibits activity of the GI tract and generally acts to balance parasympathetic activity. Sympathetic innervation originates in the celiac, superior mesenteric, inferior mesenteric, and hypogastric ganglia (Rogers, 2005). If sympathetic activity is blocked, leaving the parasympathetic activity unopposed, hypermotility and diarrhea may result. This is the likely mechanism for the diarrhea associated with celiac plexus block (Mercadante, 2002).

The presence of serum proteins, blood, or excessive amounts of mucus in the bowel contributes to diarrhea.

Most diarrheas in AIDS patients are due to infection. Although some pathogens are those that also infect immunocompetent patients, most are opportunistic infections. Cytomegalovirus and cryptosporidiosis are the most common forms of diarrhea in HIV-infected patients, but other protozoan, viral, fungal, and bacterial infections are also seen in this population (Cohen et al., 2001).

Discontinue any laxatives and begin a clear liquid diet to promote bowel rest. It is helpful to avoid very hot and very cold foods, as well as any milk products. Gradually, add semisolids such as bananas, rice, applesauce, and crackers or plain toast. The diet can be advanced as tolerated. Encourage a gluten-free diet to reduce abdominal cramping, and avoid fatty foods, whole grain products, and fresh fruits and vegetables.

Monitor hydration status by tracking intake and output. Most diarrhea in palliative care other than HIV-associated diarrhea is rarely of sufficient amount or duration to require rehydration (Sykes, 2003). When rehydration is necessary, oral hydration is preferred. The rehydration solution should contain glucose, electrolytes, and water. Use commercial sports drinks (e.g., Gatorade) or dextrose and electrolyte solutions available at pharmacies (e.g., Resol, Rehydralyte, Pedialyte). As an alternative, make a solution of ½ teaspoon salt, ½ teaspoon baking soda, and 4 tablespoons sugar in 1 liter of water (Carpenito, 2000). The World Health Organization’s recommended rehydration solution is 2 g of salt plus 2 g of sugar in 1 liter of water. This can be flavored with lemon juice if desired (Waller & Caroline, 2000). Homemade solutions should be used within 24 hours of preparation. Intravenous or hypodermoclysis replacement may be required if the patient is unable to tolerate sufficient oral intake.

It is essential to provide good skin care. Keep the perianal area clean and protected. Avoid rubbing the area with wash clothes or towels. Use a pH-balanced cleanser or warm water applied using a squeeze bottle with gentle pressure. Sitz baths also help cleanse and promote comfort. Avoid soaps, since they are drying. After cleansing, apply a moisturizer followed by a barrier that contains zinc oxide, dimethicone, or silicone. Petrolatum-based products should be avoided, since they need to be reapplied frequently (Fleck, 2005). If the patient is experiencing massive amounts of diarrhea, consider the use of a fecal incontinence bag to protect skin, decrease caregiver burden, and help control odor.

Detailed information from the patient and family is required in order to assess the potential causes of diarrhea and plan appropriate interventions. The clinician must teach the importance of prompt and detailed reporting of any changes in bowel patterns:

Frequently monitor the patient’s bowel status, hydration status, and level of comfort. If diarrhea continues after instituting a treatment, appropriate changes must occur in the treatment plan. Determine if the cause was not correctly diagnosed or if a different treatment might be more effective. Encourage patients whose diarrhea continues for several days to keep intake and output records. This will assist in evaluating the need for supplemental oral or parenteral fluids.

At all times the patient is evaluated for comfort, including abdominal pain due to gas or GI spasm and discomfort associated with skin excoriation. Encourage the patient to describe the type of abdominal discomfort so that appropriate interventions are prescribed. Teach good skin care to prevent skin excoriation and instruct the patient and caregivers to report skin discomfort or any changes in the condition of the skin.